EGG DORMANCY AND SYNCHRONIZATION OF LARVAL FEEDING WITH HOST PLANT DEVELOPMENT IN 3 NOCTUID (LEPIDOPTERA) SPECIES

The implication of dormancy at the time alimentary connections are either restored or closed was investigated in three univoltine species of a single ecological group: Archanara sparganii (Esper), Archanara geminipuncta (Haworth) and Nonagria typhae (Thunberg) (Lepidoptera: Noctuidae). The two main host-plants, Phragmites australis (Cavanilles) and Typha (L.) spp. are rhizomatous monocotyledons which produce aerial shoots on which the insects feed in spring. Dormancy was initiated in the egg stage. It took place in the summer after a few days of embryonic development. Under natural conditions, diapause was completed towards the end of the year but larvae did not hatch before early spring in southern Europe. The upper temperature thresholds for diapause development were high for all three species: 21-degrees-C for A. sparganii and N. typhae, 13-degrees-C for A. geminipuncta. The intensity of diapause increased when dormancy was initiated at 21-degrees-C instead of 11-degrees-C. The response is specific and more marked for A. sparganii than for the other two species. Plant tissues are physically and chemically altered at the onset of the flowering phase in early summer. Feeding stopped at this period as the insects entered into diapause. The duration of this non-feeding phase is under control of diapause intensification for A. sparganii and N. typhae, coupled with a lower dormancy threshold development for A. geminipuncta. Larval activity was thus limited to spring in warm locations where eggs are deposited in early summer. In cooler habitats, were the host plant flowering phase and moths flights are delayed, larval activity occurs later in the year and is reported to extend through the winter season.